Method of fabricating polysilicon, thin film transistor, method of fabricating the thin film transistor, and organic light emitting diode display device including the thin film transistor

Abstract

A thin film transistor, a method of fabricating the thin film transistor, and an organic light emitting diode (OLED) display device equipped with the thin film transistor of which the thin film transistor includes a substrate, a buffer layer disposed on the substrate, a first semiconductor layer and a second semiconductor layer disposed on the buffer layer, a gate electrode insulated from the first semiconductor layer and the second semiconductor layer, a gate insulating layer insulating the gate electrode from the first semiconductor layer and the second semiconductor layer, and source and drain electrodes insulated from the gate electrode and partially connected to the second semiconductor layer, wherein the second semiconductor layer is disposed on the first semiconductor layer.

What is claimed is: 
     
       1. A thin film transistor, comprising:
 a substrate; 
 a buffer layer formed on the substrate; 
 a first semiconductor layer and a second semiconductor layer disposed on the buffer layer, the second semiconductor layer being formed on the first semiconductor layer; 
 a gate electrode disposed on the substrate and insulated from the first semiconductor layer and the second semiconductor layer; 
 a gate insulating layer to insulate the gate electrode from the first semiconductor layer and the second semiconductor layer; and 
 source and drain electrodes insulated from the gate electrode and connected to the second semiconductor layer, 
 wherein the second semiconductor layer comprises a channel region corresponding to the gate electrode, and 
 wherein crystal grains in the channel region of the second semiconductor layer are larger than crystal grains in a region of the first semiconductor layer corresponding to the gate electrode. 
 
     
     
       2. The thin film transistor of  claim 1 , wherein the first semiconductor layer and the second semiconductor layer are polysilicon layers crystallized from amorphous silicon by a metal catalyst. 
     
     
       3. The thin film transistor of  claim 1 , wherein the first semiconductor layer is a first super grain silicon (SGS) crystallization region and the second semiconductor layer is a second SGS crystallization region. 
     
     
       4. The thin film transistor of  claim 1 , wherein the first semiconductor layer comprises more metal catalyst than the second semiconductor layer. 
     
     
       5. The thin film transistor of  claim 1 , wherein the thin film transistor comprises:
 the buffer layer is disposed directly on the substrate; 
 the first semiconductor layer is disposed directly on the buffer layer; 
 the second semiconductor layer is disposed directly on the first semiconductor layer; 
 the gate insulating layer is disposed to cover at least the first semiconductor layer and the second semiconductor layer; and 
 the gate electrode is disposed on the gate insulating layer above the second semiconductor layer. 
 
     
     
       6. The thin film transistor of  claim 5 , wherein the gate insulating layer covers the entire surface of the substrate. 
     
     
       7. The thin film transistor of  claim 1 , wherein
 the buffer layer is disposed directly on the substrate; 
 the gate electrode is disposed directly on the buffer layer; 
 the gate insulating layer is disposed to cover at least the gate electrode; 
 the first semiconductor layer disposed on the gate insulating layer above the gate electrode; and 
 the second semiconductor layer is disposed on the first semiconductor layer. 
 
     
     
       8. The thin film transistor of  claim 7 , wherein the gate insulating layer covers the entire surface of the substrate. 
     
     
       9. An organic light emitting diode (OLED) display device, comprising:
 a substrate; 
 a buffer layer formed on the substrate; 
 a first semiconductor layer and a second semiconductor layer disposed on the buffer layer; 
 a gate electrode disposed on the substrate and insulated from the first semiconductor layer and the second semiconductor layer; 
 a gate insulating layer to insulate the gate electrode from the first semiconductor layer and the second semiconductor layer; 
 source and drain electrodes insulated from the gate electrode and connected to the second semiconductor layer; 
 an insulating layer disposed on the substrate to cover the source and drain electrodes; and 
 a first electrode, an organic light emitting layer, and a second electrode disposed on the insulating layer, the first electrode being connected to one of the source and drain electrodes, 
 wherein the second semiconductor layer comprises a channel region corresponding to the gate electrode, and 
 wherein crystal grains in the channel region of the second semiconductor layer are larger than crystal grains in a region of the first semiconductor layer corresponding to the gate electrode. 
 
     
     
       10. The device of  claim 9 , wherein the first semiconductor layer and the second semiconductor layer are polysilicon layers crystallized from amorphous silicon by a metal catalyst. 
     
     
       11. The device of  claim 9 , wherein the first semiconductor layer is a first super grain silicon (SGS) crystallization region and the second semiconductor layer is a second SGS crystallization region. 
     
     
       12. The device of  claim 9 , wherein the first semiconductor layer comprises more metal catalyst than the second semiconductor layer. 
     
     
       13. The device of  claim 9 , wherein
 the first semiconductor layer is disposed on the buffer layer; 
 the second semiconductor layer is disposed on the first semiconductor layer; 
 the gate insulating layer is disposed on the substrate to cover at least the first semiconductor layer and the second semiconductor layer; 
 the gate electrode is disposed on the gate insulating layer.